The manufacture of a honeycomb structure makes use of a stack of sheets 1 as shown in FIG. 1. Each of such same-format sheets is initially coated on one of its faces, e.g. face 1a, with equidistant stripes of glue 2 at a pitch p and extending generally parallel to one another and to a longitudinal median axis such as x--x'.
As shown in FIG. 2, the sheets 1 are then stacked on top of one another and in the same orientation so that the stripes of glue on each sheet are pressed against the non-glued face of the sheet immediately beneath it.
In order to obtain a cellular structure, the superposed sheets are, in addition, disposed in an alternating offset configuration perpendicular to the general direction of the stripes 2 by an amount corresponding to one half of the pitch (1/2p) of the stripe spacing.
A stack of sheets 1 made of in this way is then placed in a press which either directly or indirectly causes the stripes of glue to melt in order to stick the sheets together.
The prior technique of making the stack, as described in French patent number FR-A-No. 1 496 628, for example, has been to superpose the sheets running from a reference abutment 4 against which one edge of each sheet is applied parallel to the axis x--x' (FIG. 2).
This stacking technique has proved unsatisfactory for at least two main reasons.
The sheets 1 used are generally obtained from thin films, plies, or strips having little strength of their own, in particular against twisting. As a result, each sheet suffers from cutting distortion and it is impossible to guarantee accurate superposition merely by using an abutment 4.
In general, the machines for applying the successive stripes of glue 2 are not capable of ensuring that the pitch p between successive stripes 2 is highly accurate.
These two reasons give rise to a relative positioning errors, which can sometimes be large, between the stripes of glue on successive sheets in a stack, such that the subsequent gluing operation is faulty and unsuitable for obtaining a cellular structure having uniform cells.
These two reasons are the cause of the difficulties encountered in using automatic manufacturing means to obtain assembled structures with regularly alternating stripes of glue.
The present invention seeks to remedy the above drawbacks by providing a novel machine for forming a flat stack of sheets having a predetermined identical format.